2 Answers
2

To begin with, early game Slark is essentially about as menacing as a paper napkin. Slark needs a pretty decent baby sitter to survive early game without heavy harassment. After Slark gets to level 6 things get trickier, but the fact remains that Slark has no survivability when faced with nukes.

So the effective counter heroes will deal heavy amounts of burst damage and essentially kill Slark before he has time to fully finish his combination of death pact, shadow dance, and leech enough stat points through essence shift.

While you may not always be able to team up to kill a hero, it is still recommended to try to wrangle at least 1 other teammate to assist. But given your criteria, and whether with support or without you will need to provide truesight. So wards, or dust if you intend on going 1 on 1.

Heroes

Bane Elemental - brain sap, fiend's grip, follow up with another brain sap - items to get in the mean time, necronomicon so that the minions can pound away while you disable

Leshrac - between diabolic edict and pulse nova Slark will have a pretty hard time standing directly next to you or even using pounce. On the off chance you are pounced on split earth should be like shooting fish in a barrel to land. And you still have lightning storm to cast.